Membrane technologies such as microfiltration (MF), ultrafiltration (UF), nanofilitration (NF), and reverse osmosis (RO) have been widely used for water purification because they are energy efficient, cost-effective and simple to operate. Membrane filtration based on reverse osmosis (RO) is one of the most promising ways to desalinate seawater or brackish water, and thin film composite (TFC) or thin film nanocomposite (TFNC) membranes including ultra-thin active layers on porous supports have been widely used for this application. In TFC membranes, the active layer plays an important role in controlling water and salt transport properties, while the support layer provides enough mechanical strength to endure high operating pressure. Cross-linked aromatic polyamides prepared by interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) have been used as an active layer in commercial desalination membranes.
Enhanced water flux through the membrane contributes to reducing overall operating energy during the membrane filtration process. Although some aromatic polyamide TFC membranes have very high salt rejection (≧99%), new active layers have been developed with a goal of improving water flux while retaining this high salt rejection. For example, crosslinked polyamide membranes have been embedded with nanoparticles such as zelolite or silica, which are physically incorporated into the polymeric matrix.